摘要
Artificial structures provide an efficient method to generate acoustic vortices carrying orbital angular momentum(OAM) essential for applications ranging from object manipulation to acoustic communication. However, their flexibility in terms of chirality control has thus far been limited by the lack of reconfigurability and degrees of freedom like spin–orbit coupling. Here we show that this restriction can be lifted by controlling the individual on–off states of two coherent monopolar sources inside a passive parity-time-symmetric ring cavity at an exceptional point where the counter-propagating waves coalesce into one chiral eigenmode. One of the sources satisfies the chirality-reversal condition, generating a travelling wave field fully decoupled from and opposite to the chiral eigenmode, while the other source is phase-shifted such that the wave generated by the first source can be canceled out, and the remaining sound field circulates in the same direction as the chiral eigenmode. Such non-Hermitian selective excitation enables our experimental realization of acoustic vortex emission with switchable OAM but free of system reconfiguration. Our work offers opportunities for chiral sound manipulation as well as integrated and tunable acoustic OAM devices.
携带轨道角动量的声涡旋在物体操控和声通信等方面有着重要的价值,而人工结构则为声学轨道角动量的产生提供了一种有效的手段.但是,相关器件的实际应用始终受限于声学人工结构可重构能力和调控自由度的匮乏.本文展示了一种突破这一制约的高效方案:对于工作在手性奇异点处的无源宇称时间对称环形腔体,仅通过控制其内2个单极点源的开关状态,就可以实现轨道角动量方向的灵活切换.点源1满足手性反转条件,能够产生与非厄米简并模式解耦、手性相反的纯净行波声场;点源2产生的相应行波分量可以与该行波声场形成干涉相消,从而令叠加后的声场具有与非厄米简并模式相同的手性.这种非厄米选择性激发机制使得涡旋辐射声场的手性切换无需依赖任何系统重构过程或复杂电路控制,有望为手性声场调控以及集成、可调声学轨道角动量器件的开发带来新的机遇.
作者
Tuo Liu
Shuowei An
Zhongming Gu
Shanjun Liang
He Gao
Guancong Ma
Jie Zhu
刘拓;安烁威;顾仲明;梁善军;郜贺;马冠聪;祝捷(Key Laboratory of Noise and Vibration Research,Institute of Acoustics,Chinese Academy of Sciences,Beijing 100190,China;Department of Mechanical Engineering,The Hong Kong Polytechnic University,Hong Kong,China;The Hong Kong Polytechnic University Shenzhen Research Institute,Shenzhen 518057,China;Institute of Acoustics,School of Physics Science and Engineering,Tongji University,Shanghai 200092,China;Division of Science,Engineering and Health Studies,College of Professional and Continuing Education,The Hong Kong Polytechnic University,Hong Kong,China;Department of Physics,Hong Kong Baptist University,Hong Kong,China)
基金
supported by Research Grants Council of Hong Kong(C6013-18G,15211918,and 15205219)
the National Natural Science Foundation of China(11774297)
support from the National Natural Science Foundation of China(12104383)
Internal Research Fund of The Hong Kong Polytechnic University(ZZLC)
supported by Hong Kong Research Grants Council(12302420,12300419,and 22302718)
the National Natural Science Foundation of China(11922416 and 11802256)
Hong Kong Baptist University(RC-SGT2/18-19/SCI/006)。
作者简介
Tuo Liu received his Ph.D.degree in Mechanical Engineering from the Hong Kong Polytechnic University in 2018.He is currently an associate professor at the Institute of Acoustics,Chinese Academy of Sciences.His research interest includes physical acoustics,acoustic artificial structures,and non-Hermitian acoustics;Corresponding author:Jie Zhu received his Ph.D.degree in Materials Engineering from the Pennsylvania State University in 2008.He is currently a full professor at Tongji University.His research focuses on structured acoustic materials and metamaterials,and acoustic imaging technology and system.E-mail address:jiezhu@tongji.edu.cn(J.Zhu).
